As personal electronic devices, such as laptop computers, tablets, smartphones, or head-mounted displays and other wearable computing devices (e.g., glasses, visors, watches, wristbands, etc.) become increasingly sophisticated, people are able to interact with such devices in new and interesting ways. For example, many personal electronic devices include touch interfaces that allow users to interact with these devices according to physical touch. A personal electronic device can also include one or more cameras located such that an image of the user's face can be captured by the cameras.